Many analytical devices, such as electron microscopes, are used to image the topography and surface properties of a substrate. These devices utilize a focused beam of electrons to illuminate a substrate. Sources of these electron beams are often contained in the tips of the analytical device.
Electron point sources, which may be utilized in these analytical devices, are well known. These electron point sources, often on the order of the atomic scale and adapted to provide field emission of coherent electron beams, have been described in, e.g., “Coherent point source electron beams”, Hans-Werner Fink, Werner Stocker, and Heinz Schmid, Journal of Vacuum Science and Technology B, Volume 8, Number 6, Nov./Dec. 1990, pp. 1323-1324, in “Unraveling nanotubes: field emission from an atomic wire,” A. G. Rinzler, J. H. Hafner, P. Nikolaev, L. Lou, S. G. Kim, D. Tomanek, P. Nordlander, D. T. Colbert and R. E. Smalley, Science, 269, pp. 1550-1553 (1995), and in “Carbon nanotubes are coherent electron sources”, Heinz Schmid, Hans-Werner Fink, Applied Physics Letters, Volume 70, Number 20, 19 May 1997, pp. 2679-2680. The first reference discloses a tungsten tip terminated with an atomically perfect pyramid of tungsten atoms as the electron emitter. The second and third references disclose a carbon nanotube as the electron emitter.
By way of further illustration, U.S. Pat. No. 5,654,548 (“Source for intense coherent electron pulses”) discloses how such sources can be used for one type of electron microscopy. The entire disclosure of this United States patents is hereby incorporated by reference into this specification.
Electron beams have been used in constructing microscopes. For example, U.S. Pat. No. 6,005,247 (Electron beam microscope using electron beam patterns) discloses “An electron beam microscope includes an electron beam pattern source, a vacuum enclosure, electron optics, a detector and a processor.” U.S. Pat. No. 6,043,491 (Scanning electron microscope) discloses “A scanning electron microscope in the present invention, by employing a retarding method and suppressing interferences between an electron beam and secondary electrons or back scattered electrons, makes it possible to obtain a clearer SEM image with a higher resolution.” The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Field emitted electron beams are also useful in many types of vacuum microelectronic devices, as described in “Vacuum Microelectronics,” edited by Wei Zhu, (John Wiley & Sons, New York, 2001).
Fabrication of specialized tips used in scanning electron microscopes and atomic force microscopes is well known to those skilled in the arts. For example, U.S. Pat. No. 6,020,677 (Carbon cone and carbon whisker field emitters) discloses “Carbon cone and carbon whisker field emitters are disclosed. These field emitters find particular usefulness in field emitter cathodes and display panels utilizing said cathodes.” U.S. Pat. No. 5,393,647 (Method of making superhard tips for micro-probe microscopy and field emission) discloses “Forming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon.” The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
The prior art sources of atomic point source electron beam emitters typically must be operated at very low pressures, on the order of about 10-8 to 10-10 Torr, to protect them from disruptive contamination, chemical degradation, or destructive ion bombardment by residual gas ions. This often requires the use of complicated, expensive, and cumbersome equipment.
Carbon-based nanotubes may be configured as superconducting nano-channels. Nanotubes are resilient and have nanometer-scale, sharp tips. As such, they are useful for making micro-probe tips of microscopy devices, e.g., scanning tunneling microscope and atomic force microscope. The dimensions of carbon-based nanotubes, ideally having a single atom at the tip apex, but typically being 3 to 10 atoms in diameter at the tip, allows the tip to be positioned close enough to a conducting substrate so that a tunneling current flows between the tip and the substrate under an applied bias voltage. This tunneling current is similar to the tunneling of electrons across a barrier as described by the Josephson tunneling effect, which is obtained from a system comprising two layers of superconductive material separated by a barrier. The two layers are either connected by a very narrow conductive bridge, or are separated by a layer of nonconductive material. When this system is under superconducting conditions (low temperature), a tunneling effect takes place, in which a superconducting current or super current flows across the barrier between the superconductive layers.
In the case of carbon-based superconducting nanotubes, the barrier is the repulsive force of the Meissner effect between the superconducting carbon-based nanotube and substrate. The Meissner effect is the ability of a material in a superconducting state to expel all magnetic fields therefrom (i.e., such a superconductor is perfectly diamagnetic and exhibits a permeability of zero). Reference may be had to “The Further Inventions of Daedalus”, by David E. H. Jones, Oxford Press, 1999. In the section relating to “Electric Gas Light on Tap” (pages 174-175) the author describes methods for exploiting the Meissner effect of evacuated superconducting tubes for purposes of residential electric beam-based power distribution. Further reference may be had, e.g., to U.S. Pat. No. 4,975,669 (Magnetic bottle employing Meissner effect). The entire disclosure of this United States patent is hereby incorporated by reference into this specification. Atomic force microscopes, which rely on the repulsive force generated by the overlap of the electron cloud at the tip's surface with electron clouds of surface atoms within the substrate, negate the need of conducting substrates to obtain the same effect.
As used herein, the term “nanotube” refers to a hollow structure having a diameter of from about 0.3 to about 10 nanometers, and a length of from about 3 to about 10,000 nanometers. In general, such nanotubes have aspect ratios of at least about 1:10 to about 1:1000. Carbon-based nanotubes are hollow structures composed between 95-to 100% of carbon atoms. In general, the most commonly studied forms of nanotubes have physical properties such that they conduct electricity better than copper. Typically, carbon nanotubes have tensile strength 100 times that of steel. Carbon nanotubes become superconductors at very low temperatures. Nanotubes may be fabricated from materials other than carbon, e.g., Tungsten disulphide, Molybdenum disulphide, and Boron nitride. Carbon nanotubes may be capped with metallic cores. Carbon nanotubes can be doped with other elements, e.g. metals.
Carbon-based nanotubes may be either single-walled nanotubes (SWNT) or multi-walled nanotubes (MWNT). A MWNT includes several nanotubes each having a different diameter. Thus, the smallest diameter nanotube is encapsulated by a larger diameter nanotube, which in turn, is encapsulated by another larger diameter nanotube.
The prior art sources of atomic point source electron beam emitters typically must be operated at very low pressures, on the order of about 10-8 to 10-10 Torr, to protect them from disruptive contamination, chemical degradation, beam scattering or destructive ion bombardment by residual gas ions. This often requires the use of complicated, expensive, and cumbersome equipment.
Carbon-based nanotubes are used to form superconducting nanochannels for steering and channeling very fine electron beams or other charged particles. In order to preserve near perfect vacuum and ultra-clean conditions, the outlet ends of the superconducting nanochannels are sealed with electron transparent nano-membranes.
Fabrication of specialized tips comprising carbon-based nanotubes and its use in scanning electron microscopes and atomic force microscopes is well known to those skilled in the arts. For example, U.S. Pat. No. 6,020,677 (Carbon cone and carbon whisker field emitters) discloses “Carbon cone and carbon whisker field emitters. These field emitters find particular usefulness in field emitter cathodes and display panels utilizing said cathodes.” U.S. Pat. No. 5,393,647 (Method of making super hard tips for micro-probe microscopy and field emission) discloses “Forming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon.” The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
Electron transparent nano-membranes are well known to those skilled in the art. Reference may be had, e.g., to U.S. Pat. No. 6,300,631 (Method of thinning an electron transparent thin film membrane on a TEM grid using a focused ion beam), U.S. Pat. No. 6,194,720 (Preparation of transmission electron microscope samples), U.S. Pat. Nos. 6,188,068, 6,140,652, 6,100,639, 6,060,839, 5,986,264, 5,940,678 (Electronic transparent samples), U.S. Pat. Nos. 5,633,502, 4,680,467, 3,780,334 (Vacuum tube for generating a wide beam of fast electrons), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
The prior art sources of carbon-based nanotube applications for microscopy devices typically consist of attaching a carbon-based nanotube to the tip of a microscopy probe. The prior art, however, does not include microscopy probes incorporating superconducting nano-channels comprising carbon-based nanotubes, which are capable of guiding and manipulating charged particle beams for microscopy applications. In the remainder of this specification reference will be made to the use of single walled superconducting carbon nanotubes. However, it is to be understood that multi-walled superconducting carbon nanotubes may be utilized as well, as may be any other essentially atomically perfect nanotube structure, which, if not naturally superconducting, may be optionally externally coated with a thin film of superconducting material.
The semiconductor integrated circuit revolution of recent decades has been driven by drastic cost reductions in steadily improving technological capabilities, which generated very much greater offsetting gains in total market size. So far, this remarkable resource has not been widely harnessed for some key electron beam technologies of great importance to nanotechnology although some intriguing preliminary work has been done in the field of vacuum microelectronic devices. There is enormous untapped technical and commercial potential for nanotechnology-related applications involving substantial improvements in the high-leverage technologies of electron beam nano-lithography and nanometer resolution scanning electron microscopes (among others), which may be significantly improved by use of the sub-nanometer-scale electron beam systems of the present invention.
The nano-electron-beam approach to these technologies involves greatly miniaturizing the electron-beam source system to microscopic, sub-micron dimensions by use of the sub-nanometer-scale electron beam systems of the present invention, leading to reduced cost and increased performance. This approach can exploit integrated circuit manufacturing technologies for mass-producing sub-nanometer-scale electron beam systems of the present invention that each incorporate thousands of such nano-electron-beam sources into an overall system such as e.g., an electron beam nano-lithography system for writing integrated circuit patterns on substrates, and a nanometer resolution scanning electron microscope for detailed imaging of nanometer-scale structures. Such overall multi-nano-electron-beam systems would have greatly increased capabilities compared to present systems.
There are a number of major applications for such improved capabilities, including but not limited to the following:                1. Massively parallel nano-electron-beam sources may render electron beam lithography suitable or even preferable for the nano-lithography realm. This would once again enable its viability for semiconductor manufacturing, which is presently increasingly dominated by ever-more extraordinarily expensive deep UV optical lithography.        2. Massively parallel nano-electron-beam SEM (scanning electron microscopy) would be very useful for various inspection and screening operations in materials science and molecular biotechnology. In another embodiment, individual SEMs or more limited numbers of parallel SEMs of microscopic size could be developed for medical applications.        3. The above embodiments of electron-beam-based nano-lithographic and nano-SEM capabilities may be combined for purposes of economical nano-manipulation, nano-processing (e.g., welding, cutting, deposition), and nano-assembly operations involving a wide range of nanostructures, such as carbon nanotubes.        4. Massively parallel nano-electron-beam sources may prove useful for ultra-high density, high speed data storage and retrieval.        5. Massively parallel nano-electron-beam sources may prove useful for small, high resolution, high speed video displays.        6. Nano-sources of nano-electron-beams hold intriguing potential for use in components for some specialized embodiments of extremely high performance analog electronic systems.        7. There are potential applications involving the ongoing quest for smaller, lighter, and more radiation-resistant sources of high-power, ultra-high-frequency, sub-millimeter-microwave beams for space and aerospace applications.        
It is an object of this invention to provide a highly miniaturized electron beam source.
It is an object of this invention to provide a highly miniaturized electron beam lens.